Railroad brakes



Sept 11, 1962 H. B. HUNTREs r-:TAL 3,053,349

RAILROAD BRAKES MQ@ NRM,

Filed Nov. 5, 1959 Sept 11' 1962 H. B. HUNTREss ET AL 3,053,349

RAILROAD BRAKES INVENTORS RD B. H'UNTRESS AS S. TAYLOR Mwm/ MOC

ATTORNEYS Sept 11, 1962 H. B. HUNTREss :TAL 3,053,349

RAILROAD BRAKES 7 Sheets-Sheet 3 Filed Nov. 3, 1959 s R MNO M mNL mum HW voi VH.. v WBS M mw mh mw/ QW A mm w wm M4 \w HT y L 1 w N Y. Nw Q ATTORNEYS Sept. 11, 1962 Filed Nov. 3, 19'59 H. B. HUNTREss ETAL 3,053,349

RAILROAD BRAKES 7 Sheets-Sheet 4 FIG. 6

l -/56 /57 `l i' Ill INVENTORS. 6 3 HOWARD B. HUNTRESS Y THOMAS S. TAYLOR mem/@M ATTORNEYS Sept 1l, 1962 H. B. HUNTRESS ETAL 3,053,349

RAILROAD BRAKES 7 Sheets-Sheet 5 Filed Nov. 5, 1959 Ohw ON% OQW HVVENToRS. HOWARD-B. HuNTRr-:ss THOMAS s. TAYLOR BY ATToRNl-:Ys

Sept. 1'1, 1962 H. B. HuNTRl-:ss ET AL 3,053,349

RAILROAD BRAKES Filed Nov. s, 1959 '7 sheets-sheet e FIG. Il

N Rr Q Q Q S s R R Q Q R/ 1Q Q Q Q/ C x O be ,S QQQ @Rw 9 5S l-I- E JNVENToRs EN HOWARD B. HuNTRE'ss Q/ Q THOMAS s. TAYLOR ATTORNEYS nite tice

3,053,349 RAILRAD BRAKES Howard B. Huntress and Thomas S. Taylor, Sutfern, N.Y., assignors to American Brake Shoe Company, New York, NX., a corporation of Delaware Filed Nov. 3, 1959, Ser. No. 850,697 S Claims. (Cl. 18S- 153) This invention relates to a brake structure for railroad vehicles. More specifically, this invention relates to a pneumatic and hydraulic system for actuating the brakes of a railroad car.

The majority of railroad vehicles now in use utilize a mechanical linkage for transmitting a braking force from an air cylinder of a pneumatic system to individual brake shoes which are suspended adjacent the wheels of the vehicle. This mechanical system is relatively heavy and incorporates an intricate linkage arrangement which introduces undesirable forces on the trucks and car body.

It is a primary object of this invention to substitute a hydraulic system for mechanical linkages now in use in railroad cars in a manner such that the hydraulic system utilizes the existing pneumatic system as a signal system and power source so that the braking action in a vehicle equipped with the present hydraulic system is compatible with railroad vehicles now in use but not provided with the present hydraulic brake system, such enabling the vehicle so-equipped` to be used in interchange and still perform its braking function when associated with cars equipped with a standard air-mechanical brake system. It is a related object to construct a hydraulic system which may be substituted for the conventional mechanical system with a minimum of modication to existing vehicle structure.

The conventional mechanical linkage system now in use on railroad cars is so arranged that braking forces are transmitted to the vehicle body, and these forces also place an eccentric load or moment on the truck bolsters of each vehicle. Such an eccentric load tends to twist the bolster, cant the vehicle wheels and thereby wear down the anges of the wheels. It is another object of this invention to incorporate a hydraulic system in a railroad car brake structure in a manner such that the stresses developed in the car body and the forces applied to the bolster by the conventional mechanical system are eliminated.

After repeated applications of the vehicle brakes over extended periods of time the individual brake shoes are worn down by frictional contact with the wheels to such an extent as to necessitate adjustment of the unactuated position of the linkage system so that the brake shoes all maintain proper clearance with their respective wheels, and so that in applying the brakes, air cylinder travel is not excessive.

It is therefore another object of this invention to incorporate in a hydraulic system for actuating railroad vehicle brakes individual hydraulically actuated cylinders, each of which includes an automatic slack adjuster mechanism for maintaining a preselected spacing between the wheel-engaging surface of a brake shoe and the opposed surface of a corresponding wheel. It is a related object to enable such a slack adjuster mechanism to pay out slack in the event that an emergency braking strain may cause a temporary over-adjustment of such an extent that the brakes would remain applied after the braking signal ceases. The ability of a slack adjuster to pay out slack in such instances is highly desirable since such over-adjustment can result in locked brakes, dragged wheels and power losses. It is another related object to utilize such an automatic slack adjuster to conserve the amount of air required by the actuating pneumatic system, to

reduce the actual consumption of air and thereby perrnit the total capacity of the pneumatic system to be reduced. Such reduction in the overall capacity of the pneumatic system enables smaller air reservoirs to be utilized, and these smaller reservoirs can be recharged in less time than present, conventional railroad brake systems which utilize mechanical linkages as the brake actuating structure.

The hydraulic system of this invention utilizes a hydraulic master cylinder, which is directly actuated by a pneumatic system assumed to be already present on the railroad car, and a plurality of individual wheel cylinders which are connected to receive hydraulic pressure from the master cylinder to engage individual brake shoes with the vehicle wheels. It is a further object of this invention to incorporate in a hydraulic system of this character a hydraulic hand pump for manually actuating the brakes. Preferably the hand pump is connected to apply a hydraulic pressure directly through the master cylinder to the individual wheel cylinders; and to afford a master cylinder construction which enables the brakes to be thus actuated by either a pneumatic force or a manually `generated force is another object of this invention.

It is yet another object of this invention to incorporate in a hydraulic hand pump a safety device which automatically limits the maximum fluid pressure which can be developed by the pump to prevent over stressing of any of the component parts of the hydraulic system by the pressure developed within the hand pump.

Gther and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred em-bodimentsof the present invention and the principles thereof and what is now considered to be the. best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

FIG. 1 is a fragmentary plan View of a part of a railroad vehicle under the frame showing the manner in which a hydraulic system constructed in accordance with this invention is incorporated with a conventional pneumatic system;

FIG. 2 is a fragmentary side elevation of a railroad vehicle with a sectional view through the truck taken in the direction of the arrows 2-2 of FIG.l;

FIG. 3 is an end elevation of a railroad vehicle which a sectional View through the truck taken in the direction of the arrows 3--3 in FIG. l;

FIG. 4 is a side elevation View, in section, of one embodiment of a hydraulic master cylinder utilized in the arrangement illustrated in FIG. l;

FIG. 5 is a side elevation View, in section, of a hydraulic wheel cylinder utilized in the arrangement shown in FIG. 1;

FIG. 6 is an elevation View, in section, of a combined hydraulic reservoir and hand pump utilized yin the hydraulic braking system constructed in accordance with lthis invention;

FIG. 7 is a somewhat schematic view showing, in section, the various component parts of the hydraulic sys- 4tem in their unactuated positions;

FIG. 8 is a somewhat schematic view showing, in section, the various component parts of the hydraulic system in the respective positions assumed subsequent to a pneumatically applied braking force;

FIG. 9 is a somewhat schematic view showing, in section, the various component parts of the hydraulic system in the respective positions assumed subsequent to the application of a manually applied braking force;

FIG. is a side elevation view, in section, of another embodiment of a wheel cylinder which can be utilized in the arrangement illustrated in FIG. 1;

FIG. 1l is a side elevation view, in section, of another embodiment of a master cylinder which can be utilized in the arrangement illustrated in FIG. 1; and

FIG. 12 is a side elevation view, in section, of another embodiment of a wheel cylinder which can be utilized in the arrangement illustrated in FIG. l.

Referring now to FIGS. l-3 of the drawings, a railroad vehicle, shown as a box car, is designated generally by the reference numeral 21. The car 21- includes an under frame UF and car trucks at either end of the car. One truck 22 is illustrated in F-IGS. 1-3. The truck 22 comprises a bolster indicated by the reference character B, two side frames SF1 and SF2, and two wheel axles WA1 and WAZ. The axles are provided with wheels W in the usual manner and are rotatably mounted in journal boxes J B on the side frames in a conventional manner.

In accordance with this invention, a plurality of individual hydraulic wheel cylinders 23, 24, 25, `and 26 are mounted adjacent each of the wheels W of the railway car 21. As illustrated in FIG. l, the side frames include brake beam slots BBS which are formed on the inner sides of the side frames and are normally employed with unit Brake beams in a conventional mechanical linkage. The wheel cylinders 23 to 26 are each formed with a projecting flange and are mounted on the brake beam slots BBS by bolts 27 which are passed through apertures in the flanges of the wheel cylinders. As best viewed in FIG. 2, brake heads BH are carried by the individual wheel cylinders and brake shoes BS are in turn mounted on the brake heads BH. The brake heads for the wheel cylinders 23 and 26 are tied together by a pair of upper and lower tie rods 28 and 29 respectively, and the brake heads for the wheel cylinders 24 and 25 are likewise tied together by a pair of upper and lower tie rods 31 and 32. The brake heads BH are mounted on the wheel cylinders in a manner such that the brake heads are movable laterally -with respect to the wheel cylinders by the connecting tie rods to take care of the lateral movement which must be permitted to the wheel and axle. This mounting arrangement may preferably include a slotted construction at the end of the -wheel cylinder pistons as will be more fully described with reference to FIG. 5.

The railroad car 21 includes a pneumatic system designated `generally by the reference numeral 33. The pneumatic system 33 includes a main airline 34 which connects each car in the train to a common source of air pressure and also includes auxiliary and emergency air reservoir tanks 35A and 35E. A brake-regulating valve 36 is connected to the main airline 34 by a conduit 37 and is connected to the auxiliary and emergency reservoir tanks by conduits 38 and 39 respectively. The pneumatic system 33 also includes a main air cylinder 411 which is connected to the brake regulating valve 36 by a conduit 42.

The main air cylinder 41 is connected to actuate a hydraulic system which includes a hydraulic master cylinder 43 and the individual wheel cylinders 23 to 26 heretofore described as being mounted on the side frames SF1 and SF2. As viewed in FIGS. 1 and 2, a shaft 44 of the main air cylinder is received within an end plate of a dust guard bellows 45 mounted at one end of the master cylinder 43. As will be described in greater detail with reference to FIG. 4 hereinbelow, the shaft 44 -is operative to move an internal piston within the master cylinder to supply pressurized hydraulic fluid to each of the individual wheel cylinders to initiate a braking action. Conduit means are connected between the master cylinder and the wheel cylinders for the purpose of transmitting such pressurized fluid. These conduit means comprise a first conduit 46 which is directly connected to the master cylinder and joined in a T-connection to a conduit 47 which extends along the length of the car 21 between the car trucks. Branch conduits 43 and 49 interconnect the conduit 47 with the wheel cylinders adjacent each of the side frames.

In accordance with this invention a hydraulic reservoir and a manually actuated hydraulic pump, which affords a hand brake, are each connected to the master cylinder 43 through a common hydraulic conduit. As viewed in FIG. 3, a tank 51 is mounted in a fixed position at one end of the boxcar 2.1. The tank 51 contains hydraulic iluid and thus affords a reservoir of hydraulic fluid for the master cylinder 43. A conduit S2 interconnects the tank 51 and the master cylinder 43. As will be described in greater detail with reference to FIG. 6, a pump is immersed within the fluid contained within the tank 51 and may be actuated by means of a hand lever 53 to pump a pressurized hydraulic iluid through the conduit 52 to the master cylinder and through the conduits 46 and 47 to move the individual brake shoes into frictional engagement with the respective wheels W of the railroad car. It will be noted that the tank 51 and the hand lever 52 are positioned so that the hand brake can be easily applied by a person standing on a ladder 54 at the end of the railroad car.

In the apparatus thus far described the elements in the pneumatic system and the car trucks represent conventional or standard structure and are present on the Inajority of lthe railroad vehicles now in use. However, in place of the mechanical linkage that would normally be connected to the main air cylinder 41 to engage the brake shoes into the wheels, a novel hydraulic system including the master cylinder 43, wheel cylinders 23 to 26, and the hydraulic hand brake has been substituted therefor.

In the operation of the braking system thus far described, a braking action is initiated by a braking signal being applied to the brake-regulating valve 36 in a known manner. Such a braking signal positions the valve to supply air from the reservoir 35A through the conduits 38 and 42 to the main air cylinder 41. The piston and shaft 44 of the main air cylinder is extended axially outwardly to force pressurized hydraulic fluid from the interior of the master cylinder 43 through the conduits 46 and 47 to the individual wheel cylinders. The pistons of the individual wheel cylinders are in turn actuated outwardly of the respective cylinders to engage the brake shoes in frictional contact with the wheels and brake the car 21. Because the wheel cylinders are mounted directly on the brake beam slots the reaction forces are transmitted to the side frames rather than the car body and bolster as in the conventional mechanical linkage. The tie rods 28-32 interconnect the two brake shoes which are applied to the wheels mounted on the same axle and shift the shoes laterally of the wheel cylinders with lateral movement of the axle. Alternatively, the brakes may be applied by a person pumping the hand lever 53 to transmit pressurized hydraulic fluid through the conduit 52 to the interior of the master cylinder 43 and thence to the individual wheel cylinders.

Each individual wheel cylinder incorporates an automatically operating slack adjuster which compensates for any wear of the brake shoes by moving the brake head and shoe nearer the wheel to maintain a predetermined spacing between the shoe and the wheel and thereby afford effective and uniform braking by all of the brake shoes throughout the useful life of the shoes.

The manually actuated hydraulic pump in the hydraulic reservoir incorporates a safety device which prevents an excessive force from being developed in the hydraulic system such as might overstress some component part of the braking system. These structural features and operational aspects of each component of the novel hydraulic system will be described in greater detail with specilic reference to FIGS. 4 to l1 inclusive of the drawings.

Referring now to FIG. 4 of the drawings, there is illustrated a detailed sectional View of the master cylinder 41. The cylinder 41 comprises a pair of end plates S6 and S7 and a tubular housing 58 which extends therebetween and provides an inner bore 60 within the master cylinder. A main piston 59 is axially reciprocable within the bore 60 and includes a shank 61 of reduced diameter which has a tapered recess at 62 formed in an end thereof. The Shaft 44 of the main air cylinder 41 is received within the recess 62 and is operative upon actuation of the main air cylinder to force the piston 59 inwardly of the master cylinder in the manner described hereinabove. The housing 58 is retained within an annular recess 63 in the end plate 56 and a recess 64 formed in the radially inner portion of an annular flange 65. The liange 65 is in turn supported from the inner face of the end plate 57. A plurality of tie rods 66 extend through apertures 67, 68, and 69 in the respective end plate 56, flange 65, and end plate 57 and nuts 71 are threaded on the ends of the tie rods to pull the end plates toward one another and retain the tubular housing 53 therebetween.

The external diameter of the piston 59 is somewhat smaller than the internal diameter of the tubular housing 58, and a long stroke diaphragm 72 is fastened to the head of the piston and the outer cylinder to provide a positive, non-leaking sealing arrangement between the piston and the outer housing. The inner ange of the diaphragm 72 is clamped between the head of the piston 59 and a pressure plate 73 by a plurality of cap screws 74. The outer ilange of the diaphragm 72 is clamped between an end plate 57 and the annular flange 65 by nuts 76. Thus, the diaphragm 72 divides the bore 60 into separate chambers 70 and 75.

The end plate 57 has a first, centrally located aperture 77 extending axially therethrough and the conduit 52, which leads to the reservoir, is threaded in the aperture 77. The end plate 57 includes an additional aperture 78, and the conduit 46, which leads to the individual wheel cylinders, is threadedly connected in the aperture 78. Thus, the piston and the long stroke diaphragm define an enclosed volume 70 within the bore 60 of the ymaster cylinder, and this enclosed volume communicates with the reservoir and the wheel cylinders through the conduits 52 and 46.

The end plate S6 is formed with a centrally located aperture 79 which extends axially therethrough and which mounts a sleeve-type bearing 81 therein. The sleeve bearing 81 in turn encircles and supports the shank 61 of the piston. The end plate 56 also includes a plurality of holes 82 which extend axially through the end plate and which are disposed radially outwardly of the central aperture '79. These holes 82 communicate the interior of the dust guard bellows 45 with that portion of the inner bore 60 which is not filled with hydraulic iluid, and thus act to vent that por-tion of the inner bore to permit free reciprocation of the piston 59 within the bore. The dust guard bellows 45 acts as a shield to prevent the entry of dust or other foreign matter in-to the inner bore as a result of such venting action through the communicating holes 82.

The dust guard bellows 45 is clamped at opposite ends to the end plate 56 and the outermost end of the shank 61 to provide a fluid-tight seal around the shank 61. The connection to the end plate 56 is afforded by a slight recess 83 in one face of the end plate and a pressure plate 84. The pressure plate 84 is interposed between the nut 71 and the end plate 56 so as to firmly clamp the outer flange of the bellows 45 which is received within the recess 83. The connection to the shank 61 is afforded by a pair of relatively thin plates S6 and 87 which receive the inner flange of the bellows 45 therebetween and which are clamped together by a plurality of cap screws 88 threaded in the outer end of the `shank 61.

The piston 59 is formed with an annular flange 89 at the base end thereof and this flange 89 serves as a support for a portion of the long-stroke diaphragm when the piston is at maximum stroke. A high rate spring stack 30 may preferably be interposed between the piston 59 and the inner face of the end plate 56 to provide compensation for temperature variations, and consequent volume variations in the hydraulic fluid during operation of the hand brake in a manner presently to be described. A return spring 91 is seated at opposite ends on the inner face of the end plate 57 and the base surface of an annular recess 92 which is formed in the head of the piston 59. The spring 91 affords a biasing force for returning the piston 59 to the position illustrated in FIG. 4 at the completion of a brake actuating stroke of the master cylinder.

Valve means, indicated generally by the reference numeral 92, are disposed within the chamber 70 adjacent the end of the conduit 52 which is connected to the hydraulic reservoir. The valve means 92 are normally open, as illustrated in FIG. 4, to communicate the chamber 70 with the hydraulic reservoir, but are movable to a closed position to interrupt the communication between the master cylinder and the reservoir during a pressuretransmitting stroke of the piston 59.

The valve means 92 include an annular housing 93 which has a flanged portion seated within a recess 94 in the inner face of the end plate 57. The annular housing 93 includes a plurality of slots 96 which form ports for communicating the chamber 70 with the conduit 52. The annular housing 93 also includes a radially inwardly projecting lip or flange 97 at the axially innermost end of the housing. A piston 98 is axially slidable within the housing 93 between the positions limited by the lip 97 and the inner faces of the end plate 57. The piston 98 has an annular groove formed in the face which engages the end plate 57, and an O-ring 99 is mounted in the groove and is compressed to provide a fluid-tight seal when the piston 9S abuts the end plate 57. In this position of the piston the communication of the bore 60 with the reservoir through the conduit 52 is interrupted. Thus, the piston acts as a valve element to regulate fluid flow through the slots 96. The surface of the piston 98 which faces the end plate 57 is also provided with a circular recess 101 and a return spring 102 is seated at opposite ends in the recess 101 and the inner face of the end plate S7. The spring 102 affords a biasing force for returning the piston 98 to the normally open position as illustrated in FIG. 4.

Another coil spring 103 is seated at one end on the surface of the piston 9S which faces the main piston 59. The other end of the coil spring 103 is seated Within a circular recess 104 formed in the head of the main piston 59. The spring 103 is so adjusted that it is just unloaded when the main piston 59 abuts the end plate 56 in the fully retracted position of the main piston 59 within the master cylinder.

While the description of the operation of the master cylinder 41 will -be described more fully hereinafter with relation -to the other components of the hydraulic system, it should be noted at this time that only a slight amount of movement of the main piston 59 inwardly of the master cylinder is required for the force developed by the spring 103 to become sufficient to overcome the force afforded by the spring 102 and move the piston 98 rightwardly, as viewed in FIG. 4, to a position wherein the O-ring 99 is compressed and `seals off the interior of the master cylinder from the hydraulic reservoir.

Referring now to FIG. 5 there is illustrated in sectional side eleva-tion an individual Wheel cylinder constructed in `accordance with this invention. In FIG. 5 the wheel cylinder is indicated generally by the reference numeral 20 and comprises a base plate 106 and a housing 107 having an inner bore 108 therein. The base plate 106 is attached to one end of the housing 107 by a plurality of cap screws 109. At the end opposite that mounting the base plate 106 the housing 107 is formed with a radially '7 inwardly projecting fiange 111 and a sleeve bearing 112 is mounted in the inner periphery of the iiange 111.

A main actuating piston 113 is slidably mounted at one end within the sleeve bearing 112 for axial movement in vand out of the bore 108.

As in the construction of 4the master cylinder 41, the wheel cylinder includes a long stroke diaphragm which affords a fluid-tight seal ybetween the main piston and the outer housing. Thus, in the wheel cylinder an outer flange of a long stroke diaphragm 114 is clamped between the housing 107 and the base plate 106. The inner flange of the long stroke diaphragm 114 is clamped between the head of the piston 113 and a plate 116 which is mounted on the piston by a plurality of fillet head screws 117. Preferably the plate 116 includes a slight flange 116F which clasps the diaphragm 114 about a rounded edge of the head of `the piston 113. The long stroke diaphragm divides the interior of the cylinder 20 into .separate chambers 118 and 119 on either side of the diaphragm.

The base plate 106 includes a sleeve member 121 which projects from an inner face of the base plate and which extends axially inwardly of the cylinder parallel to the sides of the bore 108.

The inner surface of the sleeve member defines a bore 120 and the outer surface of the sleeve member includes a plurality of radially extending lugs 122 which engage the side walls of a circular recess 123 which is formed in the head end of the piston 113. The innermost end of the sleeve member 121 abuts an annular base surface 125 of the recess 123 to limit the extent of the movement of the piston 113 axially inwardly of the housing 107. The piston 113 also includes a recess 124 formed in the base surface 125.

A return spring 126 is seated at opposite ends on the inner face of the ange 111 and the base of an annular recess 127 which is formed in the surface of the piston facing the flange 111 and biases the piston inwardly of the housing 107.

The sleeve member 121 is formed with a plurality of apertures 128 which extend radially therethrough and interconnect the chamber 119 with the inner bore 120.

The base plate 106 is formed with a central inlet opening 129, which may preferably have internal pipe threads as illustrated and which affords a connection to a conduit leading to the master cylinder 43.

A slack adjuster piston 131 is slidably mounted within the bore 120 and has one end 131B formed with a reduced diameter so as to clear the retaining ring 134. The

surface of the piston 131 which faces the inner surface of the base plate 106 is formed with an annular groove 132 and O-ring 133 is mounted therein so as to be compressed by movement of the piston 131 to the extreme leftward position illustrated in FIG. 5. Such compression of the O-ring 133 affords a fluid-tight seal which prevents any fiow of hydraulic fluid past the O-ring and to the port 129. The extent of the movement of the slack adjuster piston 131 toward the main actuating piston 113, rightwardly as viewed in FIG. 5, is limited by a snap ring 134' which is seated in an annular groove 135 formed in the bore 120.

The slack adjuster piston 131 includes an inner bore 134 in the surface facing the inlet port 129 and also includes an orifice 136 which extends axially through the head of the piston and communicates the bore 134 within the slack adjuster piston with the chamber 119. The base surface at the bottom of the bore 134 is formed with a generally concave recessed surface 137 in the area surrounding the orifice 136 and a valve 138, which is slidably mounted within the bore 134, has a generally hemispherical-shaped projection which is shaped complementary to the concave recess 137 and is engageable therein to block any fluid ow through the orifice 136. The valve includes ports 139 which extend through the body of the valve to permit fluid flow therethrough. A snap ring Cil 141 is seated in an annular groove formed in the cylindrical surface of the bore 134 and affords a support for a spring retainer 142. A return spring 143 'is seated at opposite ends on the spring retainer 142 and a recessed surface 144 of the valve. Thus, the valve 138 is biased to a normally closed position wherein the valve blocks any flow through the orice 136.

In a normally closed position of the valve, as illustrated in FIG. 5, the slack adjuster piston 131 defines an expansible chamber 140 within the portion of the bore that is confined between the slack adjuster piston and the base plate 106. The slack adjuster piston and the main actuating piston 113 define another expansible chamber therebetween which is the chamber 119 as described hereinabove. This latter chamber is sealed from the expansible chamber by the O-ring which is compressed into engagement with the inner face of the plate 106 in the disposition of the parts illustrated in FIG. 5. The force causing such compression of the O-ring 133 is generated by the return spring 126 and is transmitted through the incompressible hydraulic fluid contained in the chamber 119.

As illustrated in FIG. 2, each of the wheel cylinders is inclined at a slight angle from the horizontal. Thus, any air in the hydraulic fluid within the wheel cylinders rises to the convolution at the upper portion of the diaphragm 114. For the purpose of bleeding such air from the hydraulic system, the base plate 106 has a bleed tube 146 mounted on an inner face thereof so as to extend in close proximity to the convolution in the long stroke diaphragm. A bleeder hole 147 is formed in the base plate 106 and communicates the interior of the bleed tube 146 with a head seal on one of the cap screws 109.

The outer end of the piston 113 is formed with a T- shaped slot 148 which is adapted to receive a complementary T-shaped lug of one of the brake heads therein. The mounting arrangement afforded by the T-shaped slot permits `the brake head to slide horizontally through the T-shaped slot so that the brake head and brake shoe can move laterally of the wheel cylinder to compensate for lateral movement of the wheels and axles with respect to the side frames on which `the wheel cylinders are mounted.

While the description of the operation of the wheel cylinder will be described in relation to the operation of the other component parts of the hydraulic system of this invention hereinafter and with reference to FIGS. 7, 8 and 9 of the drawings, the manner in which the slack adjuster piston functions to take up slack and the manner in which the foot valve 138 functions to pay out slack will now be bricy described. Assuming that a hydraulic pressure is applied to the expansible chamber 140 through the inlet port 129 with the disposition of the component parts of the wheel cylinder 20 is illustrated in FIG. 5, the volume of the chamber 140 is increased by movement of the slack adjuster piston 131 rightwardly within the bore 120, as viewed in FIG. 5. Simultaneously, the force developed within the chamber 140 is transmitted through the incompressible hydraulic fluid contained in the chamber 119 defined between the main piston and the slack adjuster piston, and the main piston 113 is forced axially outwardly of the housing 107 to move the brake shoe toward the periphery of the car wheel. The adjuster piston 131 normally moves a distance which is equal to the distance D between its beveled edge 131B and the ports 128. This motion of the adjuster piston normally causes suicient motion of the output piston 113 to cause the brake shoe to be engaged in frictional contact with the periphery of the wheel and apply a `braking force to the wheel. However, as the brake shoes wear down the gap between the brake shoe and the wheel increases so that the main piston 113 must be moved outwardly of the housing some additional amount. In such a case the hydraulic pressure in the g chamber 140 moves the slack adjuster piston 131 to a position wherein the beveled edge 131B uncovers the ports 128 Ito communicate the expansible chamber 119 directly with the master cylinder through the chamber 140 and the inlet port 129. The hydraulic iiuid thus permitted to flow into the chamber 119 increases the volume of this chamber and exerts a force on the piston 113 to move the piston axially outwardly and engage the brake shoe with the car wheel.

Upon cessation of the braking etort and consequent decrease in the hydraulic fluid pressure within the chamber 148, the return spring 126 moves the main piston 113 axially inwardly of the 'housing 187 and the force of the spring 126 is transmitted through the hydraulic lluid in the chamber 119 to move the slack adjuster piston 131. This return movement of the piston continues until the slack adjuster piston is returned to the position illustrated in FIG. and in which `the O-ring is compressed to form a fluid-tight seal between the two chambers 140 and 119. However, the main piston 113 cannot return to the position illustrated in FIG. 5 because the volume of the chamber 119 was increased by the amount of the fluid which was admitted through the ports 128 on the brakeapplying stroke of the wheel cylinder. Therefore the main piston 113 does not return to the limit position wherein the annular base face 125 abuts the end of the sleeve member 121 but is stopped at a different position wherein the original clearance between the brake shoe and the wheel, which existed prior to any wearing down of the brake shoe, has been restored. The seal ailorded by the compressible O-ring 133 prevents any leakage of tluid from the chamber 119 to the inlet port 129 which would tend to increase this clearance. Thus, the cylinder 20 automatically adjusts the starting position of the brake shoe to compensate for any wearing down of the brake shoe so that on a subsequent actuation of the brakes, the brake shoe will be engaged with the wheel without requiring the slack adjuster and piston to move a greater distance than the distance D It some unusual situation should arise which would cause such over adjustment of 4the slack adjuster as to necessitate the paying out .of some slack by decreasing the volume of the expansible cham-ber 119, or in the event that it is necessary to decrease the volume of this chamber during replacement of a worn out brake shoe, the construction of the valve 138 aiords means for paying out slack by decreasing the volume of the chamber 119. In such a case it is necessary only that a force of a predetermined magnitude be applied to the outer end of the main piston 113. Such a force is transmitted through the hydraulic fluid contained within the chamber 119 and acts yon the valve 138 to overcome the bias of the return spring and unseat the valve. Hydraulic iluid then flows through the orice 136 and the orifices 139 and out the inlet port 129 to the master cylinder and alternately to the reservoir. Such a decrease of the volume of the chamber 119 permits the piston 113 to be retracted inwardly of the housing 107 to the position illustrated in FIG. 5 wherein the annular base surface 125 abuts the end 'of the sleeve member 121.

Referring now to FIG. 6, there is illustrated in sectional -side elevation the tank 51 and manually actuated hydraulic pump described hereinabove in relation to FIG. 3 of the drawings. In FIG. 6 the tank 51 is seen to comprise side walls 51S, a bottom wall 51B and a top wall 51T, which walls form a closed reservoir 151 for hydraulic iiuid. A base member 152 is mounted on the inner sur-face of the bottom wall 51B by cap screws 153 and is formed with an inner bore 154 which extends axially throughout the entire height of the base member. The base member is also formed with a second radial bore 155 which communicates with the bore 154 and the reservoir 151. The bore 155 is formed with internal pipe threads 156 by which the valve element 157 is attached to the base 152 to open or block the flow path afforded by the bore 155 between the bore 154 and the reservoir 151. The valve element 15'7 is illustrated in its normally open position in FIG. 6. The valve element 157 is part of a valve assembly 158 which has an upwardly extending tubular shaft 159 connected for rotation by a second tubular shaft 161 by means of a pin connection 162. The shaft 161 extends through a sealed aperture 160 in the top 52T of the tank and is manually rotatable by a hand lever 163.

With the valve in lthe normally open position as illustrated in FIG. 6, hydraulic fluid may gravity feed from the reservoir 151 through the conduit 52 to the master cylinder to make up for any deliciency in the volume of the fluid in the master cylinder due to `operation of the slack adjusters in the individual wheel cylinders. Also, any excess uid in the wheel cylinders may be returned to the reservoir 151 through the normally open valve by paying out the slack in the wheel cylinders as described in detail with reference to FIG. 5 hereinabove.

In accordance with this invention a manually actuated hydraulic pump, indicated generally by the reference numeral 164, is mounted on the base member 152 and immersed within the hydraulic iluid in the reservoir 151. The hand pump 164 includes a tubular housing 166 having an inner bore 167 therein and also includes a piston 168 which is reciprocable within the bore 167. The tubular housing 166 is supported on the base member 152 by an intermediate block member 169. The block member 169 is mounted on the base member 152 by a plurality of fillet head screws 171 which are passed through apertures formed in a radially projecting ilange 169F of the block. The tubular housing 166 includes a radially projecting flange 166F at the 4lower end thereof and the flanges 166F and 1691 are bolted together by a plurality of screws 172 and nuts 173.

The piston 168 is biased outwardly of the bore 167 to the limit-ing position illustrated in FIG. 6 by a coil spring 174. The coil spring 174 is seated at one end on the upper surface of the flange 166F and is seated at the opposite end on the lower surface of a radially projecting iiange 176F which projects radially outwardly from a portion of the piston adjacent the upper end thereof.

A flanged tubular housing 177 is mounted from the top of the tank by a plurality of screws 178 in a manner such that the lower end of the tubular housing abuts the upper end of the piston 168 to limit the movement of the piston outwardly of the bore 167.

The flange 176F preferably includes a stepped construction on the lower surface thereof such that the base portion of the flange is of a somewhat greater thickness than that portion on which the spring 174 is seated. This stepped construction forms a spring guide which prevents movement of the spring laterally of the ange and also provides a stronger section at the base of the flange. The lower surface of this base portion of the flange is operative to abut the upper end of the tubular housing 167 and thereby limit the movement of the piston inwardly of the housing.

The lower end portion of the piston 168 is formed with an annular groove and sealing means, such as an O-ring 179, are received within the groove to form a huid-tight seal between the piston and the bore 167. Thus, the piston denes a variable volume chamber 181 within the bore 167.

The upper end of the piston is recessed at 182 and a shaft 183 is connected within the recess by a pin-joint connection 184. The shaft 183 passes through an aperture 185 in the top of the tank and is connected to the manually actuated lever 53 illustrated in FIG. 3. A dust guard Ibellows 186 has a lower ange clamped between the top of the tank and a pressure plate 187 by the screws 178 and is connected at an upper end to the shaft 183 to seal the aperture 185 from the entry of dust or other foreign matter.

In accordance with this invention the hand actuated pump 164 incorporates an automatically operating pressure regulating device which prevents the hydraulic pressure generated within the chamber 181 from exceeding a predetermined magnitude. This pressure regulating device incorporates structure which also functions as an innet valve for the pump 164 and will now be described.

The tubular housing 166 includes a set of apertures 188 which extend radially through the housing and which constitute inlet ports for the flow of fluid from the reservoir 151 to the chamber 181. These ports 188 are formed in a lower portion of the housing which has an internal bore 189 of slightly smaller internal diameter than the bore 167, but which is open at its upper end to the chamber 181. A floating annular valve sleeve 191 which is generally U-shaped in section is slideable within the bore 189 and is operative to communicate the chamber 181 with the reservoir 151 upon either a predetermined amount of upward movement or downward movement from the neutral position shown in FIG. 6. The valve sleeve 191 is forced biased to the neutral position illustrated by an upper spring 192 and a lower stack of springs 193. The upper spring 192 is seated within the annular recess afforded by the U-shaped construction of the valve sleeve and is seated at an upper end on a spring retaining ring 194 which in turn is positioned by a snap ring 195 seated in a groove in the bore 167 adjacent the junction of the bores 167 and 189.

The lower stack of springs 193 abut the lower face of the valve sleeve and are seated on an upper face of the block member 169. A guide tube 196 for maintaining the vertical alignment of the spring stack 193 is mounted at a lower end within the block member 169 and is received within a central aperture of the annular floating valve sleeve 191. The guide tube 196 thus forms an annular chamber 197 within the portion of the bore 189 disposed between the lower face of the valve sleeve 191 and the upper face of the block member 169. Pressure relief ports 198 are formed in the lower portion of the tubular housing 166 just above the flange 166F for venting this chamber 197 to the reservoir 151 and thus permitting free vertical movement of the valve sleeve 191.

The block member 169 is formed with a central bore 199 which communicates the bore 154 in the base member 152 with the interior of the guide tube 196 and the chamber 181. A check valve 201 is axially slideable within the bore 199 and is biased upwardly by a coil spring 202 to the position illustrated in FIG. 6 wherein the check valve blocks any iiow between the conduit S2 and the chamber 181. The coil spring 202 engages the lower face of the check valve 201 and is seated on a snap ring 203 which is positioned in an annular groove in the bore 154. The check valve 201 includes a compressible ringtype seal 204 which is compressed into fluid tight, sealing relation with an annular shoulder formed adjacent the end of the bore 199. The check valve and the compressible seal 204 are thus self-energized by a pressure within the conduit 52, assuming that the valve 158 is closed, to prevent any bleed oi of the pressure in the conduit through the pump 164 tothe reservoir 151.

The overall operation of the hydraulic system will now be described with particular reference to FIGS. 7, 8, and 9. In these figures the master cylinder, reservoir, and hand pump, and an individual wheel cylinder are somewhat schematically illustrated. The structural parts however correspond to the parts described in detail with reference to FIGS. 4, 5, and 6 and like reference numerals are used to designate like parts but with the addition of the suftix A in FIG. 7, B in FIG. 8, and C in FIG. 9.

In FIG. 7 the disposition of the parts illustrated is that assumed with the system at rest but with the automatic slack adjuster mechanism of the wheel cylinder A operative to compensate for a slight amount of brake shoe wear as noted by the legend. Thus, it will be noted that the surface 125A of the piston 113A is slightly spaced 12 from the end of the sleeve member 121A, rather than being engaged with the end of the sleeve member as illustrated in FIG. 5, and this spacing results from a slight amount of hydraulic fluid having been trapped within the chamber 119A on some previous braking cycle or cycles.

In FIG. 7 the valve `158A in the hydraulic reservoir is open so that the reservoir communicates through the conduit 52A and the ports 96A with the chamber 70A of the master cylinder to replenish any quantity of fluid which may have been required by operation of the slack adjusters in the individual wheel cylinders.

In FIG. 8 the disposition of the parts of the hydraulic system is that assumed subsequent to a braking action resulting from an actuation of the main air cylinder of the pneumatic system. In such pneumatic actuation of the system, the air cylinder shaft 44B moves the piston 59B of the master cylinder inwardly of the cylinder and displaces hydraulic fluid from the chamber 70B to the individual wheel cylinders. The pressure generated by such movement of the piston 59B is transmitted through the hydraulic uid within the chamber 70B and acts in conjunction with the force of the spring '103B to move the piston 98B against the bias of the return spring 102B to the position wherein the sides of the piston cover the ports 96B and the sea-l 99B is compressed to a fluid-tight, sealing relation with the inner face of the end plate 57B to thereby seal ott the conduit 52B and prevent any loss of pressure from the chamber 70B. In this instance the positions of the parts of the hand pump are the same as that illustrated in FIG. 7.

In FIG. 8 the parts of the wheel cylinder 20B are illustrated as being positioned to supply hydraulic fluid from the master cylinder to the chamber 119B to compensate for some wearing down of the brake shoe. Thus, the slack adjuster piston 131B is shown engaged with the stop 134B. In this position of the slack adjuster piston the ports 128B are uncovered and hydraulic iiuid is admitted to the chamber 119B to move the main piston 113B outwardly of the cylinder and independently of any axial movement of the slack adjuster piston. Upon cessation of the braking effort, as applied by the shaft 44B, the return spring 126B is effective to move the pistons 113B and 131B leftwardly as viewed in FIG. 8 to close the ports 128B and trap the extra fluid admitted to the chamber 119B in the manner more fully described with relation to FIG. 5 hereinabove.

In FIG. 9 the disposition of the parts of the hydraulic system is that produced by actuation of the hand brake. In this instance the valve 158C is closed so that downward movement of the piston 168C to the position illustrated in FIG. 9 is effective to overcome the bias of the spring 202C and move the check valve 201C to an open position wherein the pressurized fluid within the chamber 181C is displaced from the chamber and through the conduit 52C to the master cylinder. This flow of pressurized iiuid passes through the ports 96C of the normally open valve 92C and thereafter tiows from the chamber 70C through the conduit 46C to the wheel cylinder 20C to actuate this wheel cylinder in the same manner as if the braking action were initiated by the main pneumatic cylinder.

In FIG. 9 the parts of the wheel cylinder 20C are again illustrated as being positioned to compensate for slack caused by wearing down of the brake shoe.

It is important that means be provided for compensating `for variations in temperature of the hydraulic fluid during such operation of the hand brake. Otherwise the handbrake might be applied at a low temperature and a subsequent rise in temperature could cause such an expansion in the fluid as would overstress some component part of the system. Alternatively the brakes might be applied at a comparatively high hydraulic iiuid temperature and a subsequent drop in temperature could cause contraction of the fluid and release of the brakes. In

accordance with this invention the spring stack 80 affords such compensating means. The spring stack acts as an accumulator, permitting some expansion on a rising fluid temperature, yet exerts a sufficient force on piston 59 to maintain actuating pressure in the chamber 70 during a falling fluid temperature.

The manner in which hydraulic fluid is pumped from the reservoir 151 through the conduit 52 will now be described in grea-ter detail with particular reference to FIG. 6. As illustrated in FIG. 6, the valve sleeve 191 is at a neutral position which is assumed subsequent to an intake or an up-stroke of the piston '168. Assuming that the piston 168 is moving upwardly on the intake stroke, the pressure within the chamber 181 is continuously decreased by such upward movement since this chamber is sealed by the check valve 201. The pressure differential across the valve sleeve 191 produced by such upward movement of the piston is effective to move the valve sleeve upwardly against the biasing force of the spring 192 to a position wherein the inner flange of the valve sleeve moves above the upper end of the guide tube 196 to communicate the reservoir 151 with the chamber 181 through the inlet port 188 and the annular opening thus produced between the valve sleeve and the guide tube. Upon completion of the intake stroke of the piston the pressure differential across the valve sleeve 191 ceases and the spring i192 returns the valve sleeve to the neutral position illustrated in FIG. 6, wherein the sleeve blocks flow between the chamber '181 and the ports 188.

It will be recognized that downward movement of the piston i168 is effective both to displace the fluid from the chamber 181 through the conduit 52 and to generate a pressure differential across the valve sleeve which tends to move the valve sleeve against the biasing `force of the spring stack 193 in a direction opposite that produced on the intake stroke of the pump. Thus, as viewed in FIG. 6, the pressure within the chamber 181 tends to move the valve sleeve downwardly against the biasing force of the spring stack i193. By selecting the biasing force to be exerted by this spring stack, the pressure within the chamber 181 can be limited to -a predetermined magnitude to afford the automatically operating pressure regulating feature of the pump 164 pointed out hereinabove. Thus, upon the individual wheel cylinders being actuated to positions wherein all of the brake shoes are engaged with the corresponding wheels it is possible for an operator to continue to build up pressure within the chamber 1&1 by continued pumping of the hand lever 53, illustrated in FIG. 3. It is `desirable that the pressure thus generated be limited to a predetermined, maximum amount to prevent over stressing of some of the component parts of the hydraulic system.

As the pressure in the chamber 1811 increases, the valve sleeve 191 compresses the spring stack .193 to a greater and greater extent and ultimately the valve sleeve is thus moved to a position wherein the upper edge of the outer flange of the sleeve uncovers the ports 188. In this latter position of the valve sleeve the high pressure within the chamber is vented through the ports 188 to the reservoir 151 and the maximum pressure obtainable is thus limited to that pressure which causes such compression of the spring stack. The slight decreases in the pressure within the chamber `'181 afforded by this venting action permits the sleeve valve '191 to move back to a position wherein the outer flange of the sleeve valve again covers the ports 18,8. As mentioned hereinabove the check valve 201 and the seal 204 is effective to retain the pressure developed in the conduit 52 to maintain the brakes in an applied position.

The tank 51 and the associated pump 154 thus perform a plurality of separate functions; this combined mechanism acts as a reservoir, a hand brake pump, a pressure-relief device, and a pressure-holding device.

In FIG. there is illustrated another embodiment of fa wheel cylinder constructed in accordance With this invention. The wheel cylinder illustrated in FIG. 10 incorporates a lip-type seal rather than a long stroke diaphragm type of seal as illustrated in FIG. 5. Insofar as the parts of the wheel cylinder illustrated in FlIG. l0 correspond to like parts of the `wheel cylinder illustrated in FdG. 5, like reference numerals are used but with the addition of the suffix D in FIG. l0.

`In FIG. l() a wheel cylinder is indicated generally by the reference numeral 211D and includes an outer housing 107D which is suitably joined to a base plate 106D. A piston 113D is slidable within an inner bore 168D of the housing and 'is supported by a bearing 112D mounted within an inwardly projecting flange at the end of the housing opposite that connected to the base plate. A T-shaped lug 211 is formed on the outermost end of the piston 113D and is adapted to mount a brake head and brake shoe assembly thereon in a manner such that the brake head is laterally movable with respect to the cylinder 20D.

A coil spring 126D is seated at opposite ends on an inner face of the flange 111D and a base surface of an annular recess 127D in the piston 113D. The return spring 126D biases the piston inwardly of the housing 157D to a position where the bottom of the inner cavity of the piston 113D contacts the outer yannular face of the sleeve member 121D, thus limiting the inward movement of the piston. The outermost cylindrical surface of the piston 113D is formed with a groove 214 and a resilient lip-type seal member 215 is disposed therein. The seal member 215 is of a U-shape in section and is aligned in the groove 214 so as to have one flange in engagement with the periphery of the bore 108D and another flange in engagement with the base surface of the groove 214. Thus, a fluid pressure transmitted to the central portion of the seal member 215 acts to ex the flange members in opposite radial directions to positively engage the outer flange with the periphery of the bore and the inner flange with the cylindrical surface of the base of the grove and thereby afford a fluid-tight seal between the piston and the bore 108D.

The cylinder 20D also includes an axially extending sleeve member `121D which projects from the inner face of the base plate 106D. The outer periphery of the sleeve member 121D incorporates a grooved construction which is received within an axially extending bore 123D of the piston 113D and which affords additional support for the piston within the housing. The sleeve member 121D includes an inner bore 120D and a plurality of apertures y128D extend radially through the sleeve member to communicate the interior of the sleeve member with the exterior thereof. As in the embodiment of the wheel cylinder illustrated in FIG. 5, the wheel cylinder 20D includes a slack adjuster piston 131D which is axially slidable within the bore D and which defines an expansible chamber 119D within the main piston and another expansible chamber D within the sleeve member 121D on the side of the slack adjuster piston opposite that facing the main piston. An inlet port 129D is centrally located in the base plate 106D for communicating the chamber 140D with the master cylinder. A valve 138D is spring biased to a position wherein the valve closes off an axially extending aperture 136D formed in the head of the slack Iadjuster piston.

The operation of the wheel cylinder 20D is like that described in detail with reference to the cylinder illustrated in FIG. 5 land will therefore only be briefly described at this time. Upon a fluid pressure being transmitted to the lchamber 140D the slack adjuster piston and the main piston are both moved by reason of the hydraulic fluid contained in the chamber 119D therebetween. Normally the brake shoe carried by the piston `113D is engaged with the periphery of the ca-r wheel prior to such movement of the slack `adjuster piston 131D as would uncover ports 128D and communicate chamber 119D and the head end of the main piston directly with the inlet 129D.

However, if there has been sufficient wear at the face of the brake shoe on a previous braking cycle, such movement of the main and slack adjuster piston may be necessitated as to result in the slack adjuster piston moving to a position wherein such fluid flow through the ports 128D occurs. The pressurized fluid thus transmitted to the chamber 119D compensates for the wearing down of the brake shoe by moving the main piston axially outwardly while the slack adjuster piston is retained against the fixed stop 134D.

Throughout all phases of `the operation of the power cylinder 20D hydraulic fluid pressure is effective to liex the seal 215 to prevent the escape of fluid to the chamber 118D.

The valve 138D permits slack to be paid out by exerting a force of a sufiicient magnitude on the outermost end of the piston 113D in the same manner as described `in detail with reference to FIG. 5.

In FIG. ll there is `illustrated another embodiment of a master cylinder constructed in accordance with this invention. AThe master cylinder is indicated generally by the reference numeral 221 and comprises a pair of end plates `222 and 223. A tubular housing 224 is mounted at opposite ends within annular grooves 226 and 227 formed in the inner faces of the respective end plates 222 and '223. The opposite ends of the housing 224 each have an annular groove therein and a compressible seal member, shown as an O-ring 228, is positioned therein. The end plates are biased toward one another to compress the seals 228 by any suitable means.

The housing 224 forms an axially extending inner bore 229 and a piston member 231 is slidable within the bore. The end plate 222 has a large central aperture 232 and an annular shaped adapter member 233 is retained in a fixed position in the aperture, as by welds 234. The adapter member in turn includes an inner annular recess 236 which mounts a sleeve bearing 237 therein. The adapter member 233 also includes an inner annular groove 23S which is spaced axially outwardly from the recess 236, and a compressible O-ring is positioned within the groove 238. A third recess 241 is formed in the inner periphery of the adapter member at the outer end of the member and is spaced axially outwardly from the groove 239. A dust guard shield member 242 is mounted in an upper corner of the recess 241 and projects radially inwardly at a slight angle.

The piston 231 includes a disk member 243 which is fastened to the end of the shaft 244 by a cap screw 245. The shaft 244 extends axially through the adapter member 233 so as to be supported by the bearing 237 and encircled by the O-ring seal 239. The innermost edge of the dust guard member 242 engages the periphery of the shaft to scrape off any foreign matter and thus prevent such foreign matter from being transmitted to the seal or the bearing by axial movement of the piston.

A resilient annular seal member 246 is mounted on the peripheral portion of the disk 243 to afford a iluid-tight seal between the piston and the bore 229. The seal member 246 is of generally triangular shape in section and includes a recess 247 which extends radially outwardly from the innermost end of the seal member and thus adapts the seal member for mounting on the peripheral portion of the disk 243. As viewed in FIG. ll the seal member is seen to be slightly canted so as to have one edge of the outer base portion of the triangular section in engagement with the cylindrical surface of the bore 229. This construction of the seal member 246 enables a servo sealing action to be obtained whereby higher pressures within the chamber 248 act to flex the seal member 246 into tighter engagement with the cylindrical surface of ythe bore.

The piston 231 is illustrated in its maximum retracted position wherein the disk 243 abuts the inner edge of' the adapter member 233. In this position of the piston the piston uncovers an aperture 251, which extends radially through the housing 224, in a manner such that the chamber 248 directly communicates with the conduit 52, connected to a fitting 252 mounted within the aperture 251 and the hydraulic reservoir.

The end plate 223 is formed with a central aperture 253 which extends axially therethrough and which mounts a fitting 254 therein. The fitting 254 is in turn adapted to be connected to the conduits 46 and 47 leading to the individual wheel cylinders.

In the operation of the master cylinder illustrated in FIG. ll, the piston 231 is moved axially inwardly of the housing 224 by the air cylinder shaft 244 in the same manner as the master cylinder illustrated in FIG. 4. This inward movement of the piston moves the seal member 246 past the inlet port 251 to block any iiuid flow between the chamber 248 and the hydraulic reservoir. Continued movement of the piston inwardly of the cylinder pressurizes the fluid within the chamber 248 to flex the seal member 246 into a tight, sealing relation with the inner cylindrical surface 0f the bore and displace hydraulic fiuid throught the outlet port 253 to the individual wheel cylinders and thereby engage the brake shoes with the car wheels. Upon cessation of the braking effort by the main cylinder the biasing force of the return springs in the individual wheel cylinders and the air cylinder 41 are eifective to return the piston 231 to the position illustrated in FIG. l1. It will be recognized that a return spring can be incorporated in the master cylinder 221 if desired. The slight angle at which the seal member 246 is mounted on the disk 243 permits any excessive quantity of hydraulic fluid within the chamber 249 to flow past the flexible seal member and into the chamber 248 during the retraction stroke of the piston.

In the fully retracted position of the piston 231 as illustrated in FIG. ll, the manually actuated hand pump within the hydraulic reservoir may supply pressurized hydraulic liuid through the inlet port 251 to the chamber 243 of the master cylinder and through the outlet port 253 to actuate the individual wheel cylinders.

Another embodiment of a wheel cylinder is illustrated in FIG. l2 and designated generally by the reference numeral 301. In this instance the cylinder 301 includes an outer housing defined by an end cap 302 which mates with a cylinder piece 303 at respective radially projecting flange portions 304 and 306. The flanges 304 and 306 are formed with a plurality of circumferentially spaced openings 307 and 308, and Allen head cap screws 309 are passed therethrough and have nuts 311 threaded on the ends of the cap screws to clamp the end cap to the cylinder piece. The end cap 302 and cylinder piece 303 are formed with an internal bore 312 of constant internal diameter which extends for substantially the entire length of the cylinder 301.

The cylinder piece 303 includes an inwardly projecting flange 313 at the end opposite that mating with the end cap 302, and the flange 313 terminates in an axially extending sleeve 314 which forms a support for a main piston 316 which is reciprocal within the bore 312. As illustrated in FIG. l2, the sleeve 314 includes a relatively short radially projecting flange 317 on the inner circumference thereof. A bushing 318 is disposed on the inner side of the flange 317 and retained in position by a retaining ring 319, while a scraper-type seal guide 321 is disposed in the annular recess defined on the opposite side of the flange 317.

The piston 316 includes a rod portion 322 which is slidable within the bushing 318 and engaged by the scraper-type seal 321. The outermost end of the rod portion 322 is formed with a T-shaped lug 323 for mounting a brake head and brake shoe thereon.

The end cap 302 includes a passageway 324 which is adapted to be connected to the master cylinder to supply hydraulic Huid from the side of the cylinder 301 to the interior thereof.

A slack adjuster piston 326 is formed with an axially projecting flange 327 at the outer periphery thereof and this flange adapts the piston 326 for reciprocation within the portion of the bore 312 defined by the end cap 302. The extent of reciprocal movement of the piston 326 is limited in one direction by abutment of the piston with an inner surface 323 of the end cap 332 and in the opposite direction by engagement of the flange 327 with a ring 329 mounted within an annular groove formed in the side walls of the bore 312.

Thus, it will be seen that the main and slack adjuster pistons 316 and 326 define a rst expansible chamber 331 therebetween and within the bore 312. The piston 326 also defines a second expansible chamber 332' within the portion of the bore 312 formed in the end cap 332.

In accordance with this invention the piston 316 is of a slightly smaller diameter than the diameter of the bore 312 and includes an axially extending sleeve 333 which affords a skirt on which a portion of a long stroke diaphragm 334 rests. The long stroke diaphragm 334 is clamped between the mating portions of the end cap 332 and 363 and extends across the bore 312 as illustrated in FIG. 1'2. Thus, the diaphragm 334 is continuous and requires no connection to the piston 316. It will be apparent from FIG. l2 that the diaphragm 334 forms a uidtight seal at one end of the chamber 331.

As a safety measure, an additional sealing device is preferably formed between the piston 316 and the bore 312 to maintain effective operation of the wheel cylinder 3G11 in the event that the diaphragm 334 should be ruptured. The structure affording such a safety seal includes a radially projecting flange 336 formed at the extremity of the skirt 333. An annular groove 337 is formed in the liange 336 and a resilient member, preferably an O-ring 333 fitted with a Teflon cap, is disposed within the groove 337 so as to be engaged in fluid-tight sealing relation with both the side walls of the bore 312 and the groove 337.

Provision is made 'for bleeding the chamber 331 to remove any air which may become entrapped therein. The structure for accomplishing such bleeding action includes an unloaded sealing screw 339` 'threaded within an opening 341 formed in a side wall of the end cap 302. In this instance the bleed screw is closely adjacent the convolution in the diaphragm 334 so that no auxiliary bleed tube -is required.

The side walls of the end cap 332 are also formed with a plurality of circumferentially spaced slots 342 which form passageways for transmitting hydraulic fluid from the chamber 332 to the chamber 331 subsequent to a predetermined extent of movement of the piston 326 as will be presently described. In the position of the piston 326 as illustrated in FIG. 12 flow of fluid through the passageways 342 is effectively blocked by the flange 327. Additional sealing means in the form of an O-ring 343 disposed within an annular recess 344 formed in the piston 326 are provided for insuring that there be no seepage of fluid from the chamber 331 to the chamber 332 in the illustrated position of the piston 326.

The two pistons are biased to the positions illustrated by a pair of coil springs 346 and 347, each of which is seated at opposite ends on the piston 316 and the llange 313. In this instance the coil springs 346 and 347 are oppositely wound so as to minimize twisting of the diaphragm 334 from spring rotation caused by compression of the springs during an output stroke of the wheel cylinder.

A filtered drain and vent opening 34S is formed in the cylinder piece 303 on the air side of the piston 316 for venting this portion of the bore 312 during reciprocation of the piston 316.

The wheel cylinder 301 is effective to compensate for slack caused by a wearing down of the brake shoes in the following manner. Application of high pressure hydraulic fluid to the interior of the chamber 332 through the passageway 324, which is connected to the master cylinder,

13 forces the piston v326 away from the end cap; right-wardly as illustrated in FIG. l2. Such movement of the piston 326 transmits a force through the hydraulic fluid trapped between the main and adjuster pistons and causes movement of the piston 316. Normally the brake shoe carried by the brake head mounted on the lug 323 is engaged with the car wheel prior to such movement of the piston 326 as would communicate the chamber 332 with the slots 342, and thus the chamber 331. Thus, upon cessation of the braking effort as applied by the master cylinder the return springs 346 and 347 are effective to return the pistons to the positions illustrated in FIG. l2 with no change in the volume of the chamber 331. However, if there has been sufficient wear at the face of the brake shoe on a previous braking cycle, such movement of the main piston 316 and slack adjuster piston 326 may be necessitated as to result in the slack adjuster piston moving Ito a position wherein this piston uncovers the slots 342 so as to communicate the chamber 332 with the chamber 331. Thus, the slack adjuster piston 326 may move from a first position wherein the passageways 342 are blocked to a second position, 4against the retaining ring 329, wherein the passageways communicate rwith the chamber 332. In this second position the pressurized hydraulic fluid increases the volume of the chamber 331 to force the main piston outwardly of the bore until the brake shoes are engaged with the car wheel. As in the other embodiments of the wheel cylinders, the return springs exert a biasing force through the hydraulic fluid contained within the chamber defined between the two pistons to move the adjuster piston back to a position wherein the piston blocks W' ythrough the passageways 342 to thereby trap the increased volume of hydraulic fluid between the two pistons.

ln some cases it may be necessary to decrease the axial l spacing between the two pistons, and valve means 351 are provided in the adjuster piston 326 to enable this to be accomplished. The piston 326 may preferably be formed with an arched configuration in the central portion thereof, as illustrated, so that a bored rivet 3'52 may be disposed within an opening 353 extending through the piston 326;.; in a manner such as to obviate any possibility of interfenj ence of the projecting portions of the rivet with other component parts of the wheel cylinder 301. In this instance the rivet 352 is formed with an internal L-shaped bore 354 and a small helical spring 356 is seated at opposite ends on the piston 326 and a retaining ring 357 mounted at one end of the rivet. The spring 356 normally biases the rivet 352 to the position illustrated in FIG. 12 wherein an O-ring 358 in the head of the rivet is compressed to sealing relation about the periphery of the aperture 353 to prevent any ow of duid through the bore 354 of the rivet. However, a force of a predetermined magnitude may be exerted on the main piston 316 in the direction indica-ted by the arrow X to pressurize the fluid within the chamber 331 and unseat the rivet 352 to thereby decrease the volume of the chamber 331 by transferring fluid through the bore 354 to the cham-1 ber 332.

Thus, a hydraulic system constructed in accordance with this invention can be readily installed on railroad vehicles presently in use as a replacement for the conventional mechanical linkage, and such installation requires only a minimum of modification to the existing vehicle structure. The braking action afforded by the hydraulic system of this invention is compatible with that obtained with vehicles utilizing a mechanical linkage so that a vehicle which incorporates a hydraulic brake system described herein can be present in the same train with cars having brakes operating in accordance with the standard air-mechanical system. The brakes may be applied either by the pneumatic `system or by a manually actuated hand pump. In the latter instance the hand pump utilizes the fiuid pressure distributing system afforded by the master cylinder and conduit connections to the individual 19 wheel cylinders to minimize the conduit connections required for manually applying the vehicle brakes. The manually actuated hydraulic pump is mounted within the hydraulic reservoir in a novel manner, and a safety device is incorporated in the hydraulic pump to regulate the maximum pressure obtainable with the pump and thereby prevent overstressing of any component parts of the over-all hydraulic system. An automatic operating slack adjuster is incorporated in each individual wheel cylinder to take up any slack caused by wearing down of the brake shoes. Additionally, each individual wheel cylinder incorporates mechanism for paying out slack in the event that some emergency strain causes an overadjustment of the slack adjuster.

Hence, while we have illustrated and described the preferred embodiments of our invention, it is to be understood that these are capable of variation and modification, and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claims.

We claim:

l. In a braking system for a railroad vehicle of the kind wherein brake shoes are engageable with the wheels of the vehicle, a pneumatic system including a main pneumatic cylinder, and a hydraulic system including a hydraulic master cylinder having a piston operatively associated with said pneumatic cylinder, a plurality of individual wheel cylinders operatively connected to the master cylinder for actuating the brake shoes into engagement with the wheels of the railroad vehicle, slack adjuster means associated with each of said individual cylinders and inclusive of means for furnishing make-up iiuid to the wheel cylinders from the master cylinder, container means defining a gravity flow reservoir for supplying the entire hydraulic Huid requirements of the system, a hydraulic hand pump, conduit means operatively connecting the reservoir and the hand pump to the master cylinder, said master cylinder having a normally open port which communicates with the conduit means, and a normally open valve means associated with said port to admit makeup fluid from said reservoir to said master cylinder, said valve means being closable by movement of said master cylinder piston as an incident to brake actuation to block fluid flow from the master cylinder to the conduit means.

2. A braking system as defined in claim l wherein said slack adjuster means include valve means for bleeding off a part of the trapped iluid to thereby increase the spacing between the wheels and the brake shoes.

3. A braking system as defined in claim l wherein said hydraulic hand pump includes pressure regulating means for automatically venting the pump to a low pressure to limit the maximum hydraulic pressure which can be developed by said pump.

4. In a railroad vehicle of the kind having car trucks and wherein each car truck includes a pair of spaced apart side frames mounting a pair of parallel extending wheel axles therebetween, which axles are free to rotate and are movable laterally within the side frame mounts, and wherein each wheel axle mounts a wheel adjacent an end thereof; a hydraulic braking system comprising, a plurality of wheel cylinders, each of which is mounted on a side frame adjacent a respective wheel, and each of which cylinders has a piston reciprocable therein, a brake shoe mounted on each piston for lateral movement across the end of the piston, a master cylinder connected to supply pressurized hydraulic fluid to each of said wheel cylinders to move the brake shoes into engagement with the car wheels, and connecting members interconnecting the brake shoes applied to the Wheels of each individual axle so that the brake shoes and connecting members move as a unit across the ends of the pistons to adjust for lateral movement of the axles with respect to the side frames.

5. In a railroad vehicle of the kind having car trucks and wherein each car truck includes a pair of spaced apart side frames mounting a pair of parallel extending Wheel axles therebetween, which axles are free to rotate and are movable laterally within the side frame mounts, and wherein each wheel axle mounts a wheel adjacent an end thereof; a hydraulic braking system comprising, a plurality of wheel cylinders, each of which is mounted on a side frame adjacent a respective wheel, and each of which cylinders has a piston reciprocable therein, a brake shoe mounted on each piston for lateral movement across the end of the piston, a master cylinder connected to supply pressurized hydraulic tluid to each of said wheel cylinders to move the brake shoes into engagement with the car wheels, connecting members interconnecting the brake shoes applied to the wheels of each individual axle so that the brake shoes and connecting members move as a unit across the ends of the pistons to adjust for lateral movement of the axles with respect to the side frames, and automatically operative slack adjuster means in said wheel cylinders for maintaining a predetermined spacing between each wheel and respective brake shoe.

6. In a railroad vehicle of the kind having car trucks and wherein each car truck includes a pair of spaced apart side frames mounting a pair of parallel extending wheel axles therebetween, which axles are free to rotate and are movable laterally within the side frame mounts, and wherein each wheel axle mounts a wheel adjacent an end thereof; a hydraulic braking system comprising, a plurality of wheel cylinders, each of which is mounted on a side frame adjacent a respective wheel, and each of which cylinders includes a piston which has a T-slot in an outer end, a brake shoe mounted in each T-slot on each piston for lateral movement across the end of the piston, a master cylinder connected to supply pressurized hydraulic iiuid to each of said wheel cylinders to move the brake shoes into engagement with the car wheels, and connecting members interconnecting the brake shoes applied to the wheels of each individual axle so that the brake shoes and connecting members move as a unit across the ends of the pistons to adjust for lateral movement of the axles with respect to the side frames.

7. In a braking system for a railroad vehicle of the kind wherein brake shoes are engageable with the wheels of the vehicle, a pneumatic system including a main pneumatic cylinder, and a hydraulic system including a hydraulic master cylinder operatively associated with said pneumatic cylinder, a plurality of individual cylinders operatively connected to the master cylinder for engaging the brake shoes with the Wheels of the railroad vehicle upon actuation of said main pneumatic cylinder, slack adjuster means associated with the wheel cylinders inclusive of means for furnishing make-up Huid to the wheel cylinders from the master cylinder, a hydraulic hand pump operatively connected to the master cylinder for passing iiuid under pressure therethrough incidental to actuating the individual cylinders independently of the pneumatic system, a single reservoir for supplying the entire hydraulic iiuid requirements of the system, said reservoir being in communication with the hand pump and a1'- ranged for supplying hydraulic fluid under a gravity head to the master cylinder, and a normally open ow control valve means interposed between the reservoir and the master cylinder for admitting fluid from the reservoir to the master cylinder when the brake is disengaged and adapted to close substantially in response to actuation of the main pneumatic cylinder.

8. In a braking system for a railroad vehicle of the kind wherein brake shoes are engageable with the wheels of the vehicle, a pneumatic system including a main pneumatic cylinder, and a hydraulic system including a hydraulic master cylinder operatively associated with said pneumatic cylinder, a plurality of individual wheel cylinders operatively connected to the master cylinder for actuating the brake shoes into engagement with the Wheels of the railroad vehicle, slack adjuster means associated with each of said individual cylinders and inclusive of means for furnishing make-up fluid to the Wheel cylinders from the master cylinder, container means dening a single reservoir for furnishing the entire hydraulic fluid requirements of the system and under gravity flow to the master cylinder, a hydraulic hand pump, and means operatively connecting the pump and the reservoir to the master cylinder including normally open Valve means in the master cylinder biased to a rst, open position Whereinthe pump and the reservoir communicates with the master cylinder, said valve means being movable by actuation of the main pneumatic cylinder as an incident to brake actuation to a second, closed position wherein the valve means block -fluid from the master cylinder to the reservoir and the hand pump.

References Cited in the tile of this patent UNITED STATES PATENTS Mahoney Nov. 27, 1934 Rymal Feb. 27, 1940 Scott Oct. 27, 1942 Hudson June 13, 1950 Nystrom et al. July 1l, 1950 McAlpine Jan. 20, 1953 Sudduth Feb. 22, 1955 Kirk Mar. 3, 1959 Hause May 19, 1959 Gelb July 7, 1959 Osvvalt Dec. 29, 1959 Frola Mar. l, 1960 FOREIGN PATENTS Great Britain Sept. 22, 1954 

